The invention relates to object range and bearing sensors.
Object range and bearing sensors are useful in numerous applications. These sensors are increasingly being implemented in automotive applications, for example to provide warnings of potential collisions with objects, including pedestrians or other vehicles.
Creating sensors that can reliably discriminate between potentially hazardous objects and objects posing no risk has been a significant challenge. Object discrimination improves as object location and velocity is further delineated. As object discrimination improves, false alarms decrease. Sensor size is also an important design consideration for many applications, particularly for automotive uses.
Conventional range and bearing determination uses lobe switching. Lobe switching is the steering of an antenna beam to scan an area. The maximum radiation or reception is sequentially switched to each of two or more directions. It is analogous to illuminating a volume of space by scanning it with a flashlight wherein only portions of the space are illuminated at any one time. Lobe switching may be accomplished mechanically or electronically. The range data is obtained by measuring the time delay. The bearing measurement is accomplished by encoding the position of the antenna, i.e., the illumination angle or lobe, and recording the object data for that angle.
Lobe switching is used to obtain bearing information when a particular bearing angle is under observation. Generally, several lobes with narrow beams are required to obtain good resolution. Resolution is increased by increasing the number of lobes scanned. The data is recorded sequentially as each lobe is scanned. This requires significant time and data memory.
Designing a small, reliable sensor capable of accurately discriminating between objects and using a minimal amount of data memory, continues to be a goal of engineers.
Embodiments of the invention include methods for measuring range and bearing of an object. In an illustrative embodiment, at least a portion of a first signal is transmitted from a sensor. The transmitted signal is reflected from an object and received by the sensor. At least a portion of the first signal is applied a first mixer and a second mixer. The received signal is applied to the first mixer and the second mixer. A second signal is generated from the first mixer, and a third signal is generated from the second mixer when the portion of the first signal that was transmitted overlaps the reflected signal at least partially. One or more of the following actions may then be performed, 1) measuring an amplitude difference between the second signal and the third signal, and determining the bearing angle based on the measured amplitude difference; 2) determining an object range based on the time delay of the second signal output; and 3) measuring a phase difference between the second signal and the third signal, and determining whether the object is to the right or left of boresight based on the measured phase difference.
The invention further includes a sensor for object range and bearing measurement. An illustrative sensor includes a first mixer to mix at least a portion of a first signal with a received signal and a second mixer to mix at least a portion of the first signal with the received signal. At least a portion of the first signal is applied to the first mixer and the second mixer, and the received signal is applied to the first mixer and the second, mixer. SIgnals may be generated from the first mixer and the second mixer when a portion of the first signal at least partially overlaps the received signal. The actions listed in the preceding paragraph may then be performed using the signals generated from the mixers.